Barnyardgrass puts roots down in too many places

I have written the previous two articles about the failure to control barnyardgrass in far too many soybean[2] fields. While the barnyardgrass may not reduce soybean yields in many cases, it results in a huge increase in the soil seed bank.

I have written a lot of articles over the past couple of years about the increasing difficulty many growers and consultants are having controlling barnyardgrass in rice[3]. While we should be using the soybean crop to control barnyardgrass and reduce the soil seed bank, quite the opposite is happening in many situations.

With most herbicides, a level of 95 percent control from any given application would be considered outstanding. In fact, on most weed science rating scales for research trials, 90 percent control and above is considered “excellent.”

With the level of barnyardgrass infestation we are building in many rice fields, 95 percent control results in a grown-up mess. In these high populations, it is possible for the barnyardgrass to simply overpower everything you throw at it.

Any time we have adverse environmental conditions, one can predict that the rice crop will have more weeds than it did in a year like 2007, when everything seemed to click.

However, the difficulty controlling barnyardgrass this year would seem to go beyond just the environmental conditions. A common comment from consultants this summer was, “Ford, am I the only one who can not kill barnyardgrass this summer?” There are a lot of clean fields, but there are a lot of fields where nothing seemed to work — the later the rice was planted, the more difficult the barnyardgrass was to control.

One of the biggest surprises was the difficulty in controlling barnyardgrass in Clearfield rice. Until this year we commonly heard about how easy it was to control weeds in Clearfield rice. In far too many Clearfield fields this year, the barnyardgrass just blew right through all Newpath and Beyond treatments.

We had all sorts of combinations of prolonged wet conditions, prolonged periods where it was too windy to get treatments out timely and prolonged dry periods. Any of these can make weed control difficult.

In addition, I observed a lot of fields where spray coverage simply was inadequate. Perhaps it was due to high fuel prices, but it was obvious that spray coverage and swath width were stretched beyond acceptable limits in a lot of fields. This should not be interpreted as me indicating applicators are doing a bad job in general. However, good coverage is necessary for good weed control and it simply was not there in some situations.

Bob Scott has reported that no additional cases of resistance to Command have been confirmed in Arkansas. Two have been confirmed to date. We are putting a lot of pressure on that herbicide, but it is difficult to rotate around it.

It would make sense that the most logical situation to rotate around Command would be in Clearfield rice. However, the Clearfield fields where I see the most weed problems are the ones where Command was left off. In those fields, if the barnyardgrass is not a problem, the sprangletop is. Sprangletop is the topic for a future article.

While these comments on Command resistance may seem encouraging, barnyardgrass is simply getting more difficult to control. It doesn’t really matter if it is resistant or not if you can not kill it.

It is certainly possible that we have more resistance to all of the herbicides than we realize. We are approaching 50 percent of our rice acreage in Clearfield rice.

I predict barnyardgrass will develop resistance to the ALS-inhibiting herbicides very quickly — if not already. Barnyardgrass resistance is likely a bigger threat to the Clearfield technology than red rice resistance.

Two things are needed. One is a much better whole farm approach to barnyardgrass management and the other is new technology.